1. Field of the Invention
The present invention relates to a composition having an anthracene derivative and a method for forming a thin film in which the composition is used. In addition, the present invention relates to a method for manufacturing a light-emitting element in which electroluminescence is used.
2. Description of the Related Art
As for organic compounds, there are a wider variety of materials and more possibilities to synthesize materials having various functions depending on the molecular design, compared with inorganic compounds. Because of these advantages, photo electronics and electronics using functional organic materials have been attracting attention in recent years.
Examples of electronic devices in which organic compounds are used as functional organic materials include solar cells, light-emitting elements, organic transistors, and the like. These are devices in which electric properties and optical properties of organic compounds are utilized. In particular, tremendous progress in light-emitting elements has been made.
It is said that light emission mechanism of a light-emitting element is as follows: when a voltage is applied between a pair of electrodes with a light-emitting layer interposed therebetween, electrons injected from a cathode and holes injected from an anode are recombined in the light emission center of the light-emitting layer to form a molecular excitons, and energy is released to emit light when the molecular excitons return to a ground state. A singlet excited state and a triplet excited state are known as excited states, and it is considered that light can be emitted through either excited state.
Such light-emitting elements have a lot of material-dependant problems for improvement in element characteristics. In order to solve the problems, improvement in element structures, development of materials, or the like have been carried out.
As a problem of light-emitting elements, improvement in reliability can be given. In particular, it has been difficult to obtain a highly reliable element with the use of a blue light-emitting material that generally has high crystallinity. For example, diphenylanthracene with high fluorescence quantum efficiency has high crystallinity and can not provide a favorable film quality; accordingly, reliability of a light-emitting element that contains diphenylanthracene is low. In order to obtain a material having lower crystallinity and higher stability, a phenylanthracene derivative as an anthracene derivative has been studied (for example, see Patent Document 1).